Chapter 8 Population Ecology

POPULATION DYNAMICS AND CARRYING CAPACITY  Most populations live in clumps although other patterns occur based on resource distribution. Figure 8-2

Changes in Population Size: Entrances and Exits  Populations increase through births and immigration  Populations decrease through deaths and emigration

Age Structure: Young Populations Can Grow Fast  How fast a population grows or declines depends on its age structure. –Prereproductive age: not mature enough to reproduce. –Reproductive age: those capable of reproduction. –Postreproductive age: those too old to reproduce.

Limits on Population Growth: Biotic Potential vs. Environmental Resistance  No population can increase its size indefinitely. –The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources. –Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

Exponential and Logistic Population Growth: J-Curves and S-Curves  Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off. Figure 8-4

Animation: Exponential Growth PLAY ANIMATION

Video: Logistic Growth PLAY VIDEO

Exponential and Logistic Population Growth: J-Curves and S-Curves  As a population levels off, it often fluctuates slightly above and below the carrying capacity. Figure 8-4

Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size  Members of populations which exceed their resources will die unless they adapt or move to an area with more resources. Figure 8-6

Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size  Over time species may increase their carrying capacity by developing adaptations.  Some species maintain their carrying capacity by migrating to other areas.  So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

Population Density and Population Change: Effects of Crowding  Population density: the number of individuals in a population found in a particular area or volume. –A population’s density can affect how rapidly it can grow or decline.  e.g. biotic factors like disease –Some population control factors are not affected by population density.  e.g. abiotic factors like weather

Types of Population Change Curves in Nature  Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically. –Stable: fluctuates slightly above and below carrying capacity. –Irruptive: populations explode and then crash to a more stable level. –Cyclic: populations fluctuate and regular cyclic or boom-and-bust cycles. –Irregular: erratic changes possibly due to chaos or drastic change.

Types of Population Change Curves in Nature  Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources. Figure 8-7

Case Study: Exploding White-Tailed Deer Populations in the United States  Since the 1930s the white-tailed deer population has exploded in the United States. –Nearly extinct prior to their protection in 1920’s.  Today million white-tailed deer in U.S. pose human interaction problems. –Deer-vehicle collisions (1.5 million per year). –Transmit disease (Lyme disease in deer ticks).

REPRODUCTIVE PATTERNS  Some species reproduce without having sex (asexual). –Offspring are exact genetic copies (clones).  Others reproduce by having sex (sexual). –Genetic material is mixture of two individuals. –Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly. –Major advantages: genetic diversity, offspring protection.

Reproductive Patterns: Opportunists and Competitors  Large number of smaller offspring with little parental care (r- selected species).  Fewer, larger offspring with higher invested parental care (K- selected species). Figure 8-9

Reproductive Patterns  r-selected species tend to be opportunists while K-selected species tend to be competitors. Figure 8-10

Survivorship Curves: Short to Long Lives  The way to represent the age structure of a population is with a survivorship curve. –Late loss population live to an old age. –Constant loss population die at all ages. –Most members of early loss population, die at young ages.

Survivorship Curves: Short to Long Lives  The populations of different species vary in how long individual members typically live. Figure 8-11

Animation: Life History Patterns PLAY ANIMATION